The best theoretic thermodynamic efficiency of internal combustion engines is obtained by a constant volume process as is well known in the prior art.
It is also well known that during low load operation much larger spark advance angles are required than comparatively at full load. Particular large spark advance is required to efficiently utilize the fuel energy in heavily diluted charges in order to avoid an excessively delayed end of heat release. Under diluted charge air/fuel mixtures are understood which contain air excess and/or recirculated exhaust gases. Large spark advance has several known disadvantages, namely severe scatter in the heat release of consecutive combustion cycles and increased emissions.
A large spark advance, which can be up to 50.degree. before top dead center, the combustion even differs widely from the desired constant volume cycle.
As a countermeasure, so called "servo igniting means" have been proposed, whereby a part of the charge, composed at least partially by an air/fuel mixture, is ignited in an ignition chamber, communicating with the main combustion chamber of the combustion engine.
Among a particularly wide variety of such igniting means a relatively recent state of the art is described in DE OS No. 29 16 285 and also in U.S. Pat. No. 4,327,681.
The amount of charge, burning in the ignition chamber should ignite the charge in the main combustion chamber in a faster and more intensive manner, whereby an approach towards a constant volume process can be realized in the main combustion chamber of the engine.
The mentioned devices have a severe draw back in that their improvement advances the art very little and their production costs, for an efficient solution are very high in comparison with the conventional properly adapted spark plug.
Also in the prior art of spark plugs, comprising ignition chamber higher than desired pumping losses, transfer flow losses and wall temperature losses occur. Particularly in the description in German Patent OS No. 29 16 285 a multitude of partial flows, respectively transfer channels, are required to establish a vortex motion of the charge in the ignition chamber. This is particularly expensive and undesirable and furthermore reduces the originally aimed torch effect.